According to a recent survey of the U.S. electronics industry, the estimated cost to the industry in 1984 of circuit boards travelling from customer sites to field service depots, back to the factory for repair, and finally back to the customer, was over $10 billion. It was found that up to 35% of those circuit boards were not defective, due to inadequate field service test equipment and "blind swapping" of circuit boards to effect a quick temporary remedy. The survey concluded that the investment in inventory control and transportation to support blind board-swapping amounts to 10% of equipment sale price. This clearly illustrates the need for more effective test equipment to quickly and accurately pinpoint fault areas, and thus allow for more on-site repair and replacement of faulty circuit boards or components.
It is important in all troubleshooting situations to eliminate areas known to be fault-free as soon as possible, so as to narrow down the search. This process can be overly time-consuming when the equipment to be tested is treated as a whole. One of the first aims of the present invention is to allow the user to isolate particular segments of the hardware under test, for example a random access memory (RAM), a read only memory (ROM), or specific input/output (I/O) area, and to test those fully before elimination or inclusion in any further testing. This technique is known as "pre-programmed diagnostic analysis" (PPDA), which allows for a broad range of test functions that can be performed automatically in sequence with little or no user interaction.
Another important aim of the present invention is to provide an effective means of fault-finding down to component level. However, having isolated any fault to a particular area, one of the main problems associated with any further testing is the dynamic nature of the buses in any microprocessor-based equipment. The traditional prior art approach has been to exercise these buses dynamically, thus emulating the action of the microprocessor itself, but this has only met with varying degrees of success. The present invention utilises unique firmware (a combination of applications software and dedicated hardware components) with the ability to drive a normally dynamic bus (for example an address, control or data bus) with a predetermined static pattern set high (=1) or low (=0) permanently, which may be traced with ease through the unit of equipment being tested. A simple tool such as a logic probe may be used to trace a fault. This approach is termed "static-stimulus testing" (SST), which, in conjunction with pre-programmed diagnostic analysis (PPDA), makes a powerful means of troubleshooting microprocessor-based equipment.
Specialised test apparatus embodying the present invention comprises a combination of hardware components which is readily portable to the test site and which is designed to be suitable for testing a large number of different types of equipment. The system is designed for a simple set-up and ease of operation and requiring the minimum of training for field service personnel.